Secondary recovery process



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P 1964 D. R. HOLBERT 3,148,730

SECONDARY RECOVERY PROCESS Filed June 27, 1960 on. STRATUM Y1 9! l- Q l6WATER .STRATUM g gig- I PRODUCING INPUT WELL I WELL) I3 I 1 u on. BANK'3 OIL sTRATuM j I] "a a VISCOUS SLUG WATER STRATUM E IO 1 PRODUCINGINPUT WELL WELL 3 VISCOUS SLUG WATER STRATUM g INVENTOR DON R. HOLBERTMM V 4 ATTORNEYS United States Patent C) 3,148,730 SECONDARY RECOVERYPROCESS Don R. Holbert, Tulsa, Okla., assiguor, 'by mesne assignments,to Sinclair Research, Inc., New York, N.Y., a corporation of DelawareFiled June 27, 1960, Ser. No. 39,043 9 Claims. (Cl. 1669) This inventionconcerns a water drive process for recovering petroleum hydrocarbonsfrom an underground formation. More particularly, my invention relatesto a water drive method for improving the recovery of oil from anoil-bearing subterranean stratum having vertical permeability andunderlain by a water-bearing formation.

One well known secondary recovery procedure for obtaining petroleum oilfrom underground formations is the so-called water drive method in whichwater is injected into the formation from an input well and conveyedtoward an adjacent or cooperating output well to push oil to the latterwell for recovery at the earths surface. A factor of utmost economicsignificance is the amount of water that must be injected for a givenincrement of oil recovery. When the expense involved in transferringwater through the formation from an input to an output well taken withthe cost of recovering the water at the output well exceeds the value ofthe oil recovered the process is obviously uneconomical. Accordingly, itis apparent that there can be merit in any method which leads to adecrease in the amount of water necessary for recovering a given amountof oil by this technique.

In many instances a subterranean formation in which a water drive isconducted is underlain by a formation containing large amounts of Water,frequently even to the exclusion of oil, and such formations oftenexhibit vertical permeability to water. In this situation water injectedinto an input well leading to the oil-bearing formation will, in goingto the output well bypass a significant portion of the oil-bearingformation even though communication in both the input and output wellsis only with the oil-bearing formation, that is the wells do not extendinto the lower water-bearing stratum. This bypassing is by way of thewater-bearing formation and is undesirable since it greatly increasesthe amount of water which must be injected to transport oil to theoutput well for recovery. Such by-passing is due to the presence ofpaths of vertical permeability in the oil and water layers and to theabsence of flow barriers, e.g. shale, intermediate the oil andwater-bearing strata. My present method is particularly designed toobviate or reduce water bypassing in these situations.

In the water-flooding process of this invention, I provide in theunderlying water-bearing stratum, an aqueous medium which is moreviscous than the aqueous medium employed in flooding the oil-bearingformation. The water-flooding medium is then charged to the oil-bearingformation from an input well and moved toward an output well. Bycorrelating the introduction and movement of the separate media, I avoidexcessive by-passing of the oil-bearing formation by the water-floodingmedium and the latter is in effect barred or deterred from travellingfrom the input to the output well by way of the lower water layer.

The amount of the more viscous liquid in the waterbearing formation canbe varied depending upon the method of operation. Although a slug of theviscous liquid of any substantial width will afford some advantage, theslug at initial injection usually will be at least about 20 feet wide,preferably at least about 30 or 40 feet wide. This injected liquid couldoccupy completely the waterbearing formation between the input andoutput wells; however, this may be uneconomic. In any event, the viscousliquid slug will be thick enough to prevent water breaking through theslug in the lower stratum too early in the process and the longer thisbreakthrough is delayed the greater should be the benefit with respectto the waterto-oil ratio produced at the output well.

The manner of providing the viscous liquid in the Water layer can bevaried. For instance, due to the vertical permeability of the formationthe viscous liquid can be injected from an input well into theoil-bearing stratum from which the liquid will flow naturally to thelower water layer. I prefer, however, that direct communica tion withthe underlying water-bearing stratum be established through a welladjacent thereto which may w tice constitlgeihe-loweLparLofitheawgt erinput well 2r even be a separate well communicating only with thewatermformation. The viscous liquid may then be injected into thewaterbearing layer, preferably across its entire vertical facecommunicating with the well. Alternatively, a watgr input well comrn inicating only with the oil-bearing laye an be fractured t o provide lessrestricted paths of communication down to the water layer and then theviscous liqfl injected. The viscous liquid could be provided imsituahyinjecting a thickenin'gagent into the water-bearing stratum from anadjacent well.

It seems rh'o st advantageous to position the leading edge of theviscous liquid in the lower water-bearing formation somewhat ahead, sayat least about 5 or 10 feet, of the water-flooding medium introducedinto the oilbearing stratum and then continue to iw v er qunusinsdiumand the rmj nediaemuausimg neously or intermittently until theviscous slug extends at least about 5 or 10 feet ahead and behind themain bank of oil being pushed from the input towards the output well.The initial overall width of the viscous slug will usually not exceedabout 150 feet and is preferably not greater than about feet. The sizeof the slug may vary depending upon factors such as its viscosity,thickness of the water-bearing formation and flood pattern well spacing.It may be advantageous to continue injection of the viscous slug atleast until the rate of its advance has been slowed down to the rate ofadvance of the regular Water displacing the oil bank.

After the slug is formed, injection of the viscous liquid can be stoppedand the ordinary water-flooding medium introduced into the oilor boththe oiland water-bearing formations to push the oil bank and itsunderlying viscous aqueous liquid slug towards the output Well. Thisinjection will most advantageously continue until the oil bank and lowerslug reach the vicinity of the output well.

In another procedure the lower viscous slug may be completely formedbefore water is injected into the oilbearing formation. Subsequentlywater can be injected into both formations or only-into the oil stratumt6move the main oil bank towards the middle of the viscous slug. Afterthe oil bank travels away from the input well the water-flooding mediumcould be introduced into the oilor both the 0iland water-bearing stratafor continuing the recovery procedure by pushing the oil bank andunderlying viscous slug towards the output well. In any event, someportion, preferably substantially all, of the main oil bank should beabove the viscous slug for a major part of the distance travelled by theoil bank from the input to the output well.

The viscous liquid used in my process is composed predominantly of waterand preferably will be essentially the same base medium as that used inwater-flooding the oil-bearing formation and may therefore containsodium chloride. The viscosity of the thicker liquid will be greaterthan that of the water-flooding fluid. Generally, the viscosity of thethicker liquid will be in the range of about 1 to 50 centipoises,preferably about 2 to 10 centipoises, more than the viscosity of thewater-flooding 3 medium and frequently the viscosity of the latter willapproximate 1 centipoise. If the viscosity of the liquid provided in thewater-bearing formation is too great, the water-flooding medium mayfinger into the viscous slug and cause an early breakthrough due to thelow mobility of the viscous liquid and the differences in perme abilityexisting across the formation. Generally, the viscosity of the thickeraqueous liquid will not exceed about 50 centipoises.

The aqueous viscous liquid can be formed by adding to an aqueous mediuma water-dispersible, preferably organic, material. Among the organicadditives suitable for incorporation in the aqueous medium arehydroxylcontaining compounds such as sugar, glycerol, glycols, e.g.ethylene glycol; polyethylene oxides corresponding to the formula RO(C HO) H, e.g. Polyox, a high molecular solid weight polyethylene oxideresin produced by Union Carbide Chemicals Co.; polyamides of the formulae.g. PAM, a white, powdery solid material; and gear gum. Thepolyethylene oxides, however, are preferable due to their lower cost.These additives are included in the aqueous medium to form the viscousliquid used in this invention and generally the additives will not begreater than about 2% of the medium, preferably not exceeding about 1%,and the amount present will be sufiicient to provide the medium with thedesired viscosity.

The method of my invention may be better understood by reference toFIGS. 1 to 3 of the drawings which illustrate diagrammatically oneembodiment of the present invention at separate stages of operation.

FIGURE 1 shows an initial stage of my process. There is provided inputwell 10 extending through oil-bearing stratum 11 and water-containingformation 12. The output or producing well is shown at 13 and need onlyextend through the oil-bearing stratum 11. Well 10 houses tubing 15 tobe used for introducing the viscous liquid into the water-bearingformation. Strata 11 and 12 exhibit vertical permeability towards water.

Into tubing 15 I inject salt water containing about 4 lbs. per gallon ofsugar or 0.7 lbs. per gallon of PAM- 200, giving in each case a liquidmedium having a specific gravity of about 1.05 and a viscosity of aboutcentipoises, at 80 F. temperature until a bank or slug 16 of this mediumextends through the water-bearing stratum 12, across essentially itsentire vertical face and about 25 feet towards the producing well 13.Fresh water is then injected across the entire face of the oil-bearingstratum by way of the annulus between tubing 15 and the wall of well 10.aroundtubing 15 .at the .junctureof stratalLandJLtg ensure properwdisstion" -of..theduiectedsflllis1r The introduction of the water-floodingmedium into formation 11 and of the viscous liquid into stratum 12 iscontinued to maintain the leading edge of the slug 16 about 25 feetahead of the principal oil bank 17 formed in stratum 11, see FIGURE 2.These injections can continue as long as desired; however, I prefer theoperation illustrated in FIGURE 3.

Most advantageously the introduction of the viscous liquid isdiscontinued after the width of the slug is about 60 feet and extendsconsiderably to the rear of oil bank 17. Then fresh water or brine isintroduced into both the oil and water-bearing strata to maintain theoil bank 17 above the viscous slug 16 as they are pushed towards theoutput well. I prefer to continue this relationship until the oil bankreaches well 13. As the oil bank and its underlying viscous slug proceedtoward the output well water acceptance in stratum 12 is significantlylessened as compared with that occurring when the viscous slug is notpresent and accordingly the water-to-oil ratio produced at well 151decreased.

If desired, a packer can be set I claim:

1. In a method employing a water-flooding medium and cooperating inputand output wells for recovering oil from an underground oil-bearingformation underlainby a water-bearing f9 rn ia t i9 i s a id formationsexhibiting paths of vertical permeability to water between the oil andwater formation, the steps comprising introducing into the water-bearingformation a viscous aqueous medium and introducing in said water-bearingformation said water-flooding medium to move said viscous aqueous mediumtowards an output well, introducing through an input well incommunication with the oil bearing formation said water-flooding mediuminto said pillaging fpr rrra;

tion to move an oil bank towards said output well to maintain an oilbank ahead of said water-flooding medium and above said viscous aqueousmedium, introducing said water-flooding medium into both of said oilandwaterbearing formations to maintain said oil bank ahead of saidwater-flooding medium and at least a portion of said oil bank directlyabove said viscous aqueous medium over a major portion of the travel ofsaid oil bank to said output well and recovering oil from said outputwell, said viscous aqueous medium having a viscosity of about 1 to 50centipoises greater than said water-flooding medi- 2. The method ofclaim 1 in which the viscous aqueous medium has a viscosity of about 2to 10 centipoises greater than said water-flooding medium.

3. The method of claim 1 in which said oil bank travels above and behindthe leading edge of said viscous aqueous medium.

4. In a method employing a water-flooding medium and cooperating inputand output wells for recovering oil from an underground oil-bearingformation underlain by a water-bearing formation, said formationsexhibiting paths of vertical permeability to water between the oil andwater formations, the steps comprising introducing into thewater-bearing formation a viscous aqueous medium, introducing through aninputwell in cornmunication with the oil bearing formation saidwaterfloodingmedium into said oil-bearing formation to move an oil banktowards said output well, continuing introduction of said viscousaqueous mgliurnand said waterfio'odingniediurrifto maintain an oil bankahead of said water-flooding medium and above said viscous aqueousmedium, discontinuing introduction of said viscous aqueous medium,introducing said water-flooding medium into both of said oilandwaterbearing formations to maintain said oil bank ahead of saidwater-flooding medium and at least a portion of said oil bank directlyabove said viscous aqueous medium over a major portion of the travel ofsaid oil bank to said output well and recovering oil from said outputwell, said viscous aqueous medium having a viscosity of about 1 to 50centipoises greater than said water-flooding medium.

5. The method of claim 4 in which the viscous aqueous medium has aviscosity of about 2 to 10 centipoises greater than said water-floodingmedium.

6. In a method employing a water-flooding medium and cooperating inputand output wells for recovering oil from an underground oil-bearingformation underlain by a water-bearing formation, said formationsexhibiting paths of vertical permeability to water between the oil andwater formations, the steps comprising introducing in the wafer-bearingformation a slug of viscous aqueous medium and introducing in saidwater-bearing formation said water-flooding medium to move said viscousaqueous medium towards an output well, introducing through an input wellin communication with the oil-bearing formation said water-floodingmedium into said oil-bearing formation to move an oil bank towards saidoutput well and to maintain said oil bank ahead of said water floodingmedium and at least a portion of said oil bank directly above and behindthe leading edge of said slug of viscous aqueous medium over a majorportion of the travel of said oil bank towards said output well andrecovering oil from said output Well, said slug of viscous aqueousmedium having a viscosity of about 1-50 centipoises greater than saidwater-flooding medium.

7. In a method employing a water-flooding medium and cooperating inputand output wells for recovering oil from an underground oil-bearingformation underlain by a water-bearing formation, said formationsexhibiting paths of vertical permeability to water between the oil andwater formations, the steps comprising providing from an input well andin the water-bearing formation a viscous aqueous medium, introducingthrough an input Well in communication with the oil-bearing formationsaid water-flooding medium into said oil-bearing formation to move anoil bank toward said output well and to maintain said oil bank ahead ofsaid water-flooding medium and at least a portion of said oil bankdirectly above said viscous aqueous medium over a major portion of thetravel of said oil bank towards said output well, and recovering oilfrom said output well, said viscous aqueous medium having a viscosity ofabout 1 to 50 centipoises 20 greater than said Water-flooding medium.

8. The method of claim 7 in which the viscous aqueous medium has aviscosity of about 2 to 10 centipoises greater than said water-floodingmedium.

9. In a method employing a water-flooding medium and cooperating inputand output wells for recovering oil from an underground oil-bearingformation underlain by a water-bearing formation, said formationsexhibiting paths of vertical permeability to Water between the oil andwater formations, the steps comprising introducing into thewater-bearing formation a slug of viscous aqueous medium and introducingsaid water-flooding medium into both of said oil-and-water bearingformations to maintain said oil bank ahead of said water-flooding mediumand at least a portion of said oil bank directly above said viscousaqueous medium over a major portion of the travel of said oil bank tosaid output well and recovering oil from said output Well, said viscousaqueous medium having a viscosity of about 1-50 centipoises greater thansaid Water-flooding medium.

References Cited in the file of this patent UNITED STATES PATENTS2,072,982 Dale Mar. 9, 1937 2,272,672 Kennedy Feb. 10, 1942 2,341,500Detling Feb. 8, 1944 2,402,588 Andresen June 25, 1946 2,731,414 BinderJan. 17, 1956

1. IN A METHOD EMPLOYING A WATER-FLOODING MEDIUM AND COOPERATING INPUTAND OUTPUT WELLS FOR RECOVERING OIL FROM AN UNDERGROUND OIL-BEARINGFORMATION UNDERLAIN BY A WATER-BEARING FORMATION, SAID FORMATIONSEXHIBITING PATHS OF VERTICAL PERMEABILITY TO WATER BETWEEN THE OIL ANDWATER FORMATION, THE STEPS COMPRISING INTRODUCING INTO THE WATER-BEARINGFORMATION A VISCOUS AQUEOUS MEDIUM AND INTRODUCING IN SAID WATER-BEARINGFORMATION SAID WATER-FLOODING MEDIUM TO MOVE SAID VISCOUS AQUEOUS MEDIUMTOWARDS AN OUTPUT WELL, INTRODUCING THROUGH AN INPUT WELL INCOMMUNICATION WITH THE OIL BEARING FORMATION SAID WATER-FLOODING MEDIUMINTO SAID OIL-BEARING FORMATION TO MOVE AN OIL BANK TOWARDS SAID OUTPUTWELL TO MAINTAIN AN OIL BANK HEAD OF SAID WATER-FLOODING MEDIUM ANDABOVE SAID VISCOUS AQUEOUS MEDIUM, INTRODUCING SAID WATER-FLOODINGMEDIUM INTO BOTH OF SAID OIL- AND WATERBEARING FORMATIONS TO MAINTAINSAID OIL BANK AHEAD OF SAID WATER-FLOODING MEDIUM AND AT LEAST A PORTIONOF SAID OIL BANK DIRECTLY ABOVE SAID VISCOUS AQUEOUS MEDIUM OVER A MAJORPORTION OF THE TRAVEL OF SAID OIL BANK TO SAID OUTPUT WELL ANDRECOVERING OIL FROM SAID OUTPUT WELL, SAID VISCOUS AQUEOUS MEDIUM HAVINGA VISCOSITY OF ABOUT 1 TO 50 CENTIPOISES GREATER THAN SAIDWATER-FLOODING MEDIUM.